The present invention relates to an apparatus and method for uniformly applying a thin film of a lubricant to the substrate surfaces in a solventless manner. The invention has particular utility in the manufacture of magnetic or magneto-optical (xe2x80x9cMOxe2x80x9d) data/information storage and retrieval media comprising a layer stack or laminate of a plurality of layers formed on a suitable substrate, e.g., a disc-shaped substrate, wherein a thin lubricant topcoat is applied to the upper surface of the layer stack or laminate for improving tribological performance of the media when utilized with read/write transducers operating at very low flying heights.
Magnetic and MO media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A magnetic medium in e.g., disc form, such as utilized in computer-related applications, comprises a non-magnetic disc-shaped substrate, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium (Alxe2x80x94Mg), having at least one major surface on which a layer stack or laminate comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers may include, in sequence from the substrate deposition surface, a plating layer, e.g., of amorphous nickel-phosphorus (Nixe2x80x94P), a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy such as chromium-vanadium (Crxe2x80x94V), a magnetic layer, e.g., of a cobalt (Co)-based alloy, and a protective overcoat layer, typically of a carbon (C)-based material having good tribological properties. A similar situation exists with MO media, wherein a layer stack or laminate is formed on a substrate deposition surface, which layer stack or laminate comprises a reflective layer, typically of a metal or metal alloy, one or more rare-earth thermo-magnetic (RE-TM) alloy layers, one or more transparent dielectric layers, and a protective overcoat layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
Thin film magnetic and MO media in disc form, such as described supra, are typically lubricated with a thin film of a polymeric lubricant, e.g., a perfluoropolyether, to reduce wear of the disc when utilized with data/information recording and read-out heads/transducers operating at low flying heights, as in a hard disk system functioning in a contact start-stop (xe2x80x9cCSSxe2x80x9d) mode. Conventionally, a thin film of lubricant is applied to the disc surface(s) during manufacture by dipping into a bath containing a small amount of lubricant, e.g., less than about 1% by weight of a fluorine-containing polymer, dissolved in a suitable solvent, typically a perfluorocarbon, fluorohydrocarbon, or hydrofluoroether. However, a drawback inherent in such dipping process is the consumption of large quantities of solvent, resulting in increased manufacturing cost and concern with environmental hazards associated with the presence of toxic or otherwise potentially harmful solvent vapors in the workplace.
Another drawback associated with the conventional dipping method for applying a thin film of a polymeric lubricant to a substrate results from the lubricant materials being mixtures of long chain polymers, with a distribution of molecular weights. Since the molecular weight of the polymeric lubricant affects the mechanical (i.e., tribological) performance of the head-disc interface, it is common practice to subject the polymeric lubricant mixtures (as supplied by the manufacturer) to a fractionation process prior to adding the lubricant to the solvent in order to obtain a fraction having a desired molecular weight distribution providing optimal tribological performance. However, such pre-fractionation undesirably adds an additional step and increases the overall process cost.
Vapor deposition of thin film lubricants is an attractive alternative to dip lubrication in view of the above drawbacks. Specifically, vapor deposition of lubricant films is advantageous in that it is a solventless process and the process for generating the lubricant vapor can simultaneously serve for fractionating the lubricant mixture into a desired molecular weight distribution, thereby eliminating the need for a pre-fractionation step. Moreover, vapor deposition techniques can provide up to about 100% bonded lubricant molecules when utilized with appropriate polymeric lubricants and magnetic and/or MO disc substrates having deposition surfaces comprised of a freshly-deposited carbon-based protective overcoat layer.
However, existing vapor deposition apparatus (e.g., Intevac VLS 100, Intevac Corp., Santa Clara, Calif.) for applying a thin layer of polymeric lubricant to a thin film data/information storage and retrieval medium, e.g., in disc form, utilize a static process/system, wherein a disc-shaped substrate is moved to a position facing the front (i.e., orifice) of a source of lubricant vapor (e.g., by means of a disc lifter) and statically maintained at that position while the lubricant film is deposited on the entire disc surface, with the lubricant film thickness being determined (i.e., controlled) by the length of the interval during which the disc surface is statically maintained facing the orifice(s) of the lubricant vapor source.
In order to control the spatial distribution, hence thickness uniformity, of the lubricant thin films obtained with such static vapor deposition process/apparatus at deposition rates of from about 1 to about 10 xc3x85/sec. for providing lubricant film thicknesses up to about 50 xc3x85, a diffuser plate for the lubricant vapor is provided intermediate the lubricant vapor source and the substrate surface, thereby adding to the system complexity and necessitating periodic maintenance of the diffuser plate for ensuring clear vapor passage through each of the openings in the diffuser plate. In addition, such static vapor lubrication systems incur a drawback when utilized as part of an in-line or similar type multi-chamber or modular system for manufacturing magnetic or MO media, in that a line-of-sight path is required for the mechanism utilized for positioning the disk surface opposite the lubricant vapor source. As a result, a path can be established for the lubricant vapor to escape from the lubricant deposition chamber into adjacent process chambers utilized for different processing functions and result in their being contaminated with lubricant vapor.
Notwithstanding the improvement in spatial uniformity of lubricant film thickness afforded by the use of a diffuser plate or similar element between the lubricant vapor source and the disk substrate surface, current vapor deposition processes for applying thin films of lubricant or other additive to substrate surfaces result in some degree of film thickness non-uniformity. It is believed that such spatial non-uniformity has dual origins, as follows:
(1) although the above-described system is nominally static, the substrate (e.g., a disc) is necessarily in motion during its placement facing the lubricant vapor source and during its removal therefrom, which motion creates a non-uniformity, i.e., a thickness gradient, across the disc surface in the direction of the motion. The extent and magnitude of the gradient is a function of the deposition rate and the speed of the mechanism utilized for placement of the disc in facing relation to the lubricant vapor source and removal therefrom; and
(2) because of the large substrate size (i.e., disc diameter) and physical constraints on apparatus dimensions, multiple lubricant vapor sources and/or vapor diffuser plates generally are necessary for obtaining thickness uniformity over the entire substrate surface. However, even in the best cases wherein multiple lubricant vapor sources and/or vapor diffuser plates are utilized, regions of greater and lesser lubricant or additive thickness are routinely obtained.
In view of the above, there exists a clear need for improved means and methodology for depositing thin films of a lubricant, e.g., a polymeric lubricant, by vapor techniques and at deposition rates consistent with the throughput requirements of automated manufacturing processing, e.g., of magnetic and/or MO data/information storage and retrieval media, which means and methodology overcome the above-described drawbacks and disadvantages of the conventional static lubricant vapor deposition technology. More specifically, there exists a need for improved means and methodology for vapor depositing thin films of lubricant (e.g., a polymeric lubricant) which provides improved lubricant film thickness uniformity over the entire deposition area of disc-shaped substrates utilized in the manufacture of such magnetic and/or MO media.
The present invention addresses and solves problems and difficulties in achieving uniform thickness lubricant thin film deposition over large area substrates by means of vapor deposition techniques, e.g., thin film polymeric lubricant deposition on disc-shaped substrates utilized in the manufacture of magnetic and/or MO media, while maintaining full capability with all aspects of conventional automated manufacturing technology therefor. Further, the means and methodology afforded by the present invention enjoy diverse utility in the manufacture of various other devices and articles requiring deposition of uniform thickness thin film lubricant layers thereon.
An advantage of the present invention is an improved apparatus for vapor depositing a uniform thickness thin film of a lubricant on at least one surface of a substrate.
Another advantage of the present invention is an improved apparatus for vapor depositing a uniform thickness thin film of a lubricant on at least one surface of a disc-shaped substrate, e.g., as part of a process/system for manufacturing magnetic and/or MO data/information storage and retrieval media.
Yet another advantage of the present invention is an improved method for vapor depositing a uniform thickness thin film of a lubricant on at least one surface of a substrate.
Still another advantage of the present invention is an improved method for vapor depositing a uniform thickness thin film of a lubricant topcoat on at least one surface of a disc-shaped substrate utilized in the manufacture of magnetic and/or MO recording media.
Additional advantages and other aspects and features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to an aspect of the present invention, the foregoing and other advantages are obtained in part by an apparatus for vapor depositing a uniform thickness thin film of a lubricant on at least one surface of a substrate, comprising:
(a) a chamber having an interior space;
(b) a substrate loader/unloader for supplying the interior space with at least one substrate and for withdrawing at least one substrate from the interior space;
(c) at least one lubricant vapor source for supplying the interior space with a stream of lubricant vapor; and
(d) a substrate transporter/conveyor for continuously moving at least one substrate past the stream of lubricant vapor from the at least one lubricant vapor source for depositing on at least one surface thereof a uniform thickness thin film of lubricant.
According to embodiments of the present invention, the chamber (a) is adapted to maintain the interior space at a pressure below atmospheric pressure; and the substrate loader/unloader (b) is adapted for providing cooling/condensation of the lubricant vapor for preventing escape thereof from the interior space of the chamber.
In accordance with particular embodiments of the present invention, the substrate loader/unloader (b) is adapted for supplying and withdrawing at least one disc-shaped substrate having a pair of opposed surfaces and the substrate transporter/conveyor (d) is adapted for mounting or gripping at least one disc-shaped substrate; the at least one lubricant vapor source (c) is elongated, with a length greater than an outer diameter of the disc-shaped substrate; and the elongated lubricant vapor source (c) comprises a closed heated chamber for accommodating liquid lubricant therein and serving as a lubricant vaporizer, the closed heated chamber fluidly communicating with at least a plurality of primary nozzle slits for supplying the stream of lubricant vapor.
According to further embodiments of the present invention, the elongated vapor source (c) further comprises a plurality of secondary nozzle slits for increased collimation of the stream of lubricant vapor, which secondary slits may be provided with cooling means.
Embodiments of the present invention include apparatus wherein a spaced-apart plurality of the elongated lubricant vapor sources (c) are arranged along a path of transport/conveyance of the at least one disc-shaped substrate within the interior space of the chamber. A first apparatus configuration according to the present invention comprises a chamber (a) in the form of a cylinder with circularly-shaped upper and lower ends; the substrate loader/unloader (b) comprises at least one combined substrate load/unload station on one of the upper and lower ends; the spaced-apart plurality of lubricant vapor sources (c) comprises a first plurality of radially extending, elongated lubricant vapor sources for depositing a thin film of lubricant on a first one of the pair of opposed surfaces of the disc-shaped substrate; the substrate transporter/conveyor (d) is adapted to move the at least one disc-shaped substrate in a circular path past each of the first plurality of radially extending, elongated lubricant vapor sources; and the spaced-apart plurality of lubricant vapor sources (c) may comprise a second plurality of radially extending, elongated lubricant vapor sources for depositing a thin film of lubricant on a second one of the pair of opposed surfaces of the disc-shaped substrate.
A second apparatus configuration according to the present invention comprises a chamber (a) in the form of an elongated, rectangularly-shaped box having a pair of longitudinally extending front and rear walls; the substrate loader/unloader (b) comprises a substrate load lock chamber connected to the chamber at a first end of said front wall and a substrate exit lock chamber connected to said chamber at a second end of the front wall; each of the spaced-apart plurality of elongated lubricant vapor sources (c) extends transversely across the front wall in the space between the load lock and exit chambers; and the substrate transporter/conveyor (d) is adapted to move the at least one disc-shaped substrate in a linear path past each of the transversely extending, elongated lubricant vapor sources.
Another aspect of the present invention is a method of vapor depositing a uniform thickness thin film of lubricant on at least one surface of a substrate, comprising the steps of:
(a) providing an apparatus comprising:
(i) a chamber having an interior space maintained below atmospheric pressure;
(ii) a substrate loader/unloader for supplying the interior space with at least one substrate and for withdrawing at least one substrate from the interior space;
(iii) at least one lubricant vapor source for supplying the interior space with a stream of lubricant vapor; and
(iv) a substrate transporter/conveyor for continuously moving at least one substrate past the stream of vapor from the at least one lubricant vapor source;
(b) supplying the interior space with a substrate having at least one surface;
(c) continuously moving the substrate past the stream of lubricant vapor and depositing a uniform thickness thin film of the lubricant on the at least one surface; and
(d) withdrawing the lubricant-coated substrate from the interior space.
According to embodiments of the present invention, step (b) comprises supplying a disc-shaped substrate having a pair of opposed surfaces; and according to particular embodiments of the invention, step (b) comprises supplying a disc-shaped substrate having a laminate of layers for a magnetic or magneto-optical (MO) data/information storage and retrieval medium formed on at least one of the pair of opposed surfaces; step (c) comprises vapor depositing a thin film of a polymeric fluorine-containing lubricant on the laminate of layers on at least one of the pair of opposed surfaces; and step (a)(iii) comprises providing an apparatus with at least one elongated lubricant vapor source having a length greater than an outer diameter of the disc-shaped substrate, the at least one elongated lubricant vapor source comprising a closed heated chamber for accommodating liquid lubricant therein and serving as a lubricant vaporizer, the closed heated chamber fluidly communicating with a plurality of nozzle slits for supplying the stream of lubricant vapor.
In accordance with particular embodiments of the present invention, step (a) comprises providing an apparatus of a first configuration wherein the chamber (i) is in the form of a cylinder with circularly-shaped upper and lower ends; the substrate loader/unloader (ii) comprises at least one combined substrate load/unload station on one of the upper and lower ends; the at least one elongated lubricant vapor source (iii) comprises a first plurality of spaced-apart, radially extending, elongated lubricant vapor sources for depositing a thin film of lubricant on a first one of the pair of opposed surfaces of the disc-shaped substrate; the substrate transporter/conveyor (iv) is adapted to move the at least one disc-shaped substrate in a circular path past each of the first plurality of spaced-apart, radially extending, elongated lubricant vapor sources; and the at least one elongated lubricant vapor source (iii) may further comprise a second plurality of spaced-apart, radially extending, elongated lubricant vapor sources for depositing a thin film of lubricant on a second one of the pair of opposed surfaces of the disc-shaped substrate.
According to another particular embodiment of the present invention, step (a) comprises providing an apparatus of a second configuration, wherein the chamber (i) is in the form of an elongated, rectangularly-shaped box having a pair of longitudinally extending front and rear walls; the substrate loader/unloader (ii) comprises a substrate load lock chamber connected to the chamber at a first end of the front wall and a substrate exit lock chamber connected to the chamber at a second end of the front wall; the at least one elongated lubricant vapor source (iii) comprises a plurality of spaced-apart, elongated lubricant vapor sources extending transversely across the front wall in the space between the load lock and exit chambers; and the substrate transporter/conveyor (iv) is adapted to move the at least one disc-shaped substrate in a linear path past each of the plurality of spaced-apart, transversely extending, elongated lubricant vapor sources.
Yet another aspect of the present invention is an apparatus for vapor depositing a uniform thickness thin film of a lubricant on a surface of a substrate, comprising:
a chamber including means for supplying a substrate to the chamber and withdrawing a substrate from the chamber; and
means within the chamber for performing pass-by vapor deposition of a uniform thickness thin film of a lubricant on a substrate surface.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.